Since a micro-electromechanical systems (MEMS) device configured by use of a movable electrode and fixed electrode has a characteristic of low loss, high insulating property and high linearity, much attention is given thereto as a key device of a next-generation mobile phone. Further, by making use of the characteristic of the MEMS device, a MEMS capacitor whose capacitance can be varied is proposed.
In the MEMS device, it is required that the peripheral portion of a movable upper electrode arranged to face a lower fixed electrode and a beam portion that resiliently supports the upper electrode should have a hollow structure. Therefore, a sacrificial layer is formed to cover the upper electrode and beam portion and a cap layer having a plurality of through-holes formed therein is formed to cover the sacrificial layer. Then, the sacrificial layer is removed to form a hollow structure. After this, a resin sealing layer of an organic material or the like is formed on the cap layer to fill the through-holes.
However, in the conventional structure, there occurs a problem that an organic material penetrates into the hollow structure of the cap layer via the through-holes in the sealing step of forming the resin sealing layer on the cap layer. If the organic material penetrates into the hollow structure, the upper electrode and beam portion are suppressed from being movable and the elements do not function in the worst case. That is, a problem of lowering the manufacturing yield and lowering the reliability occurs due to penetration of a sealing material via the through-holes formed in the cap layer that covers the upper electrode and beam portion.